The present invention relates to a hot pressure fixing device for fixing a toner image carried on a substrate.
Hot pressure fixing devices for fixing a toner image carried on a substrate are known. In such devices, which typically employ a heated fuser roller, there is a tendency for the substrate to adhere to the fuser roller unless a release agent, such as a silicone oil, is applied thereto.
In such a device as described in Japanese patent publication JP 01251074 (Canon Inc.), a hot pressure fixing device for fixing a toner image carried on a substrate comprises a heated fuser roller in contact with a back-up roller to form a nip there-between through which a substrate path extends, and a release agent application device. The application device comprises an applicator roller in rolling contact with the heated fuser roller. Release agent is conveyed from the release agent supply to the surface of the applicator roller.
In the device described in U.S. Pat. No. 4,426,953 (Kromm et al. assigned to Xerox Corporation) there is a heated fuser roller in contact with a back-up roll to form a nip there-between through which a copy substrate passes. A release agent application device is provided for applying release agent from a supply to the heated fuser roller. The release agent application device comprises a donor roller in rolling contact with the heated fuser roller, the donor roller being formed with a covering of deformable material such as silicone rubber. Release agent is conveyed by a steel-surfaced metering roll from the release agent supply to the surface of the donor roller.
In a hot pressure fixing device it is desirable that the consumption of release agent is minimized, that proper release properties are achieved, that the applied release agent is spread evenly without streaks on the heated fuser roller, and that the thickness of the release agent film on the heated fuser roller is substantially independent of the presence or absence of substrate sheets passing through the nip.
We have discovered that these objectives can more easily be achieved if the release agent application device further comprises a transfer roller in rolling contact with the applicator roller, and means for conveying release agent from the supply to the surface of the transfer roller, thereby to establish a release agent path from the supply via the transfer roller and the applicator roller to the heated fuser roller, means for defining the release agent film carried on the transfer roller in advance of the rolling contact thereof with the applicator roller, and means for defining the release agent film carried on the applicator roller in advance of the rolling contact thereof with the transfer roller.
Thus, according to the invention, there is provided a hot pressure fixing device for fixing a toner image carried on a substrate, comprising: a heated fuser roller in contact with a reaction surface to form a nip therebetween through which a substrate path extends; a release agent application device for applying release agent from a release agent supply to the heated fuser roller, and comprising: an applicator roller in rolling contact with the heated fuser roller, a transfer roller in rolling contact with the applicator roller, means for conveying release agent from the supply to the surface of the transfer roller, thereby to establish a release agent path from the supply via the transfer roller and the applicator roller to the heated fuser roller, means for defining the release agent film carried on the transfer roller in advance of the rolling contact thereof with the applicator roller, and means for defining the release agent film carried on the applicator roller in advance of the rolling contact thereof with the transfer roller.
Although one applicator roller in rolling contact with the heated fuser roller is sufficient, it is possible for more than one such applicator roller to be used. Similarly although one transfer roller in rolling contact with the applicator roller is sufficient, more than one such transfer roller may be used. It is also possible to have one transfer roller in rolling contact with another transfer roller, which in turn is in contact with the applicator roller. Even more than one such intermediate transfer roller may be used.
The release agent may be supplied to the device from a sump, from a soaked wick, or from a drip feed, such as by dripping onto a foam applicator.
The heated fuser roller has a rigid core which may be formed of a metal such as aluminum. The core carries a covering of compliant material, which may be selected from synthetic rubber materials such as silicone rubber or Viton (Trade Mark), possibly coated or covered with a PTFE or PFA-like layer. The fuser roller may be heated internally, for example by the positioning of a radiant heater within a hollow core of the roller, or by passing a heated fluid through the hollow core. Alternatively, the fuser roller may be heated externally.
The device comprises means for defining the release agent film carried on the applicator roller in advance of the rolling contact thereof with the transfer roller. In this manner, the release agent film to be applied to the heated fuser roller is stabilized, more independent of the passage of substrate sheets through the fuser nip, the consumption of release agent at the fuser nip is minimized, dust and toner debris picked up by the applicator roller are removed to avoid contaminating the oil supply and a more even oil film is supplied to the heated fuser roller.
Where the device includes a single applicator roller and a single transfer roller, there can be defined a release agent transfer coefficient (C1) between the transfer roller and the applicator roller, and a release agent transfer coefficient (C2) between the applicator roller and the heated fuser roller. Typically these transfer coefficients will be about 0.5. A proper choice of materials may result in other transfer coefficient values. These can be optimized for a given fuser system. For example, smaller transfer coefficients result in a smaller amount of oil being transferred to the heated fuser roller.
Where more than one applicator and/or transfer rollers are used, the optimum transfer coefficients should be adjusted accordingly. Each transfer roller added changes the amount of release agent transferred to the paper with a factor C/(1xe2x88x92C). Addition of a scraper blade on the extra transfer roller reduces the amount of release agent transferred to the paper by a factor 1/(1xe2x88x92C).
The means for defining the release agent film carried on the transfer roller and for defining the release agent film carried on the applicator roller, may be constituted by one or more scraper blades. The scraper blades may be fabricated from elastomer materials, such as Viton, or from metals such as steel, stainless steel or phosphor bronze. They are provided with a length co-extensive with the roller with which they are associated. The edge of the blade contacting the roller preferably has a radius of from 0.010 mm to 0.25 mm. The blade functions to control the layer of release agent picked up by the associated roller to a predetermined thickness and to remove paper dust and toner debris to prevent the latter from contaminating the release agent supply and to prevent the applied release agent being spread unevenly, causing streaks on the heated fuser roller and from there on, streaks in the image.
Preferably the device is adapted for fixing toner images carried on opposite faces of a substrate, wherein the reaction surface comprises a second heated fuser roller and a second release agent application device is provided for applying release agent from a second release agent supply to the second heated fuser roller. The second release agent application device may include a second applicator roller in rolling contact with the second heated fuser roller. The second release agent application device may further comprise a second transfer roller in rolling contact with the second applicator roller, and means for conveying release agent from the second supply to the surface of the second transfer roller, thereby to establish a second release agent path from the second supply via the second transfer roller and the second applicator roller to the second heated fuser roller.
The release agent used in the present invention is typically a functional silicone oil.
In hot pressure roller fixing devices it is desirable that residual toner and paper debris do not contaminate the supply of release agent in order to ensure that a consistent supply of release agent to the heated fuser roller is achievable. Furthermore, should there be excess release agent supplied to the heated fuser roller, it is desirable to remove this excess other than by allowing it to become transferred onto the substrate.
We have discovered that these objectives can be achieved, for example, when a cleaning device is provided comprising an intermediate roller in rolling contact with the heated fuser roller downstream of the nip to collect residual toner particles and debris from the heated fuser roller, and cleaning means for removing the toner particles and debris from the intermediate roller.
The cleaning means may be in the form of a scraper blade, a stationary cleaning pad, or a vacuum pick-up device, but most preferably comprises a moving cleaning web in contact with the intermediate roller. A suitable material for the cleaning web is a woven material such as a blend of aramid (e.g. Nomex) and polyester. The device may further comprise means for driving the cleaning web at a speed different to the circumferential speed of the intermediate roller, to improve the transfer of residual toner and debris from the intermediate roller. Additionally or alternatively, the device may further comprise means for establishing a temperature at the surface of the intermediate roller different to the temperature at the surface of the heated fuser roller, which can be particularly advantageous in improving the transfer of residual toner from the heated fuser roller towards the intermediate roller.
The intermediate roller preferably has a surface formed of a material having a surface energy higher than that of the surface of the heated fuser roller. For example, the intermediate roller has a surface formed of a material selected from silicone polymers and fluorinated polymers. The intermediate roller will usually be substantially rigid and will preferably be independently driven, but can also be driven by its rolling contact with the heated fuser roller.
Where the device is adapted for fixing toner images carried on opposite faces of a substrate, as described above, a second cleaning device may be provided comprising a second intermediate roller in rolling contact with the second heated fuser roller downstream of the nip to collect residual toner particles and debris from the second heated fuser roller, and second cleaning means for removing the toner particles and debris from the second intermediate roller.